Combined mid-infrared and hot air drying reduces energy-consumption and improves quality of jerky

Abstract: Drying was the key procedure of jerky processing, different drying methods had different economic benefits and impacts on the quality of jerky. For traditional hot air (HA) drying method has some defects in thermal efficiency, new drying method that combined mid-infrared and hot air (CMIHA) drying was investigated in this paper. CMIHA drying machine was heated directly by mid-infrared without media and convective mode, which significantly increased the rate of energy conversion and energy utilization. The thermal efficiency of CMIHA machine was 70%-80%, and the temperature drift range could be controlled under ±1℃. The structure composition, operational principle and technical characteristics of CMIHA drying machine were introduced in this study. Taking fresh beef as test material, the parameters of CMIHA drying process of jerky was optimized with range analysis, variance analysis and synthesis score analysis.Based on the heat transfer equation of combined radiation and convection, the orthogonal experiments of three factors including drying temperature (50, 60, 70℃), radiation distance (8, 12, 16 cm) and radiation intensity (0.48, 0.64, 0.80 W/cm2) were carried out with the fixed wind velocity (1 m/s) and jerky size. The indices including drying performance and benefit, shear force and color of jerky were measured. According to the range analysis, radiation distance B1 (8 cm) was preliminarily considered as the optimum dryer parameter, but drying temperature (A) and radiation intensity (C) could not be determined. According to the variance analysis, A had significant difference (p<0.1) in drying time, drying energy and b* value and C had no significant difference (p﹥0.1) in all indices, but compared with drying time, L*value and a*value, C had more important impacts on shear force, drying energy and b*value. So as for the low shear force and drying energy-consuming, A3C1 (70℃, 0.48 W/cm2) was preliminarily considered as the optimum drying parameter. Comprehensive analysis of the drying performance and benefit, quality of jerky, the appropriate drying parameter of CMIHA drying machine was A3B1C1. Through synthesis score analysis, A3B1C1 had the highest score among the ten drying parameters. Then the best CMIHA drying process was compared with mid-infrared (MI) drying (drying temperature 70℃, radiation distance 8 cm, radiation intensity 0.48 W/cm2) and HA drying (drying temperature 70℃, heat distance 8 cm, wind velocity 1 m/s), the indices including drying performance and benefit, shear force, texture profiles analysis (TPA), shrinkage rate, acid value and color were measured. The results showed that compared with MI drying and HA drying, CMIHA drying significantly reduced (p<0.05) the drying time and energy, its time-consuming and energy-consuming were only 70% and 90% of that with MI drying, 40% and 22% of that with HA drying. Besides, compared with HA drying, CMIHA drying could significantly increase (p<0.05) springiness, gumminess, chewiness, L* value, a* value, b* value and decrease (p<0.05) shear force and shrinkage rate. Compared with MI drying, CMIHA drying could significantly increase (p<0.05) gumminess, chewiness, L* value and decrease shear force and shrinkage rate, but there were no significant (p﹥0.05) differences in springiness, a* value and b* value.Based on the sensory quality, jerky with CMIHA drying could be easier accepted than that dried by MI drying and HA drying. So, compared with the traditional hot air drying, CMIHA drying could significantly increase economic benefit and quality of jerky. This study can provide a reference for the new drying method of jerky.